Posted
by
timothyon Tuesday April 10, 2001 @02:27PM
from the faster-than-a-speeding-mozilla dept.

Logic Bomb writes: "Mach 5 -- 5 times the speed of sound, or 5000 mph -- is a speed that so far has eluded jet-powered aircraft (the existing record for a production craft is about mach 2.1). NASA, however, has high hopes for its latest attempt, the X-43A. Using a booster rocket, the prototype will be accelerated to mach 5, at which point its engine will be scooping enough oxygen to power the craft at those speeds on its own. Hopefully, it will fly at speeds up to almost mach 7 for 10-15 seconds before shutting off and plunging into the Pacific. An article from the Los Angeles Times has more details." Not to be confused with the X-33 and X-34 projects.

I recall reading the fastest a MiG 25 was clocked by the west were MiG-25 recon birds flying out of Syria and chased by Israel F-4s. I'd read that they were clocked at Mach 2.7.

The MiG-25 was designed not to fight the F-15, but to intercept the XB-70 bomber, which was a Mach 3+ high altitude delta wing bomber, like a nasty Concorde with nukes. The XB-70 was canned and then development started on the B-1B, but the MiG-25 continued. The F-15 was actually designed to beat the MiG-25...not the other way around.

Maybe I'm too old to be reading slashdot but the SR-71 achieved mach 3 and used the same "scooping enough oxygen to power the craft at those speeds on its own". They called it a ramjet. Reinventing the wheel is yet another fine use of our 39% tax bracket that the Clintons invented.

Actually, the SR71 uses a hybrid turbojet/ramjet engine. At low speeds the engine acts like a standard turbojet; as speeds rise the engine begins to act more like a ramjet. Here [wvi.com] is some good info and pictures.

Here [aviation-history.com] are a couple good pictures of ramjet and scramjet engines. A scramjet is just a form of ramjet that only works above mach 1.

The other thing this plane was specifically designed to do was fly VERY long distances on small amounts of fuel, due to the special design of the engines, type of fuel, etc.

"normal" supersonic jets can go supersonic, but you're talking about going through half your total fuel supply in a matter of minutes. The SR-71 sustained these speeds for hours, over thousands of miles.
The newer F-22/F-23 generation of jets was supposed to have this new "supercruise mode" which allowed extended operation at supersonic speeds without such a heavy fuel penalty.
Unfortunately, it was another boondoggle for a defense contractor looking for big government handouts. Which they got anyway.

Concorde can fly at mach 2.01. That's almost the mach 2.1 mentioned above, and it's a *commercial passenger airliner*. I find it rather hard to believe that the military aircraft in production don't go much faster! People need to get their facts straight before spouting off technical details and trying to sound clever.

I heard about that: Concordsky. I also heard that it was probably better than Concorde. I think I heard of a documentary on the BBC within the last 8 years where they claimed a French spy plane came close to the Russian aircraft, which was why the Russian pilot dived. I think analysis of the film footage from the air show indicated another plane in close proximity.

Kinda interesting considering the recent shenannigans between the US and Chine.

The MiG-25 FoxBat (similar to F15) does mach 2.5+ (probably more like mach 3).

While that may be true, the Russian pilot that flew his FoxBat to Japan in the 70s said that they could not stay at M2.5 for very long because their engines would get too hot and sieze up. As a result, anyone who tried to go that fast would be subject to disciplinary action. It was more for chest thumping and to be able to claim that their main interceptor was faster than the US F-15.

As far as taking several states to make a banked turn, that depends on where the turn is being made. I can see that being the case for the Northeastern states. I would think they could make a U-turn within the state of Nevada.

You are correct. According to aerospaceweb [aerospaceweb.org] it first flew in 1964. At 42000, it could do 2110 mph and 650mph at sea level. The F-15 [aerospaceweb.org] first flew in 1972 and can only do 1665 at 36000ft.

Hardly. Production aircraft have no problem beating Mach 2.1. The F-16 and F-15 are both mid-Mach 2 capable, the F-111 can easily tickle the bottom side of Mach 3, and the SR-71's official speed is over Mach 3 (with unofficial speed being probably closer to Mach 4)

I'm not anti-millitary or anything, but doesn't it strike anyone as a bit twisted that with almost any new or improved technology the millitary's always standing by thinking of how it can help them kill people more efficiently? This just kind of bothers me.

On a side note, doesn't the whole mach5+ thing seem a bit pointless? Someone in an above post thought engineers shold spend more time building aquatic habitats or something. But sticking to the aerospace subject, instead of working to make the NY-LA trip 30 minutes, wouldn't it be much cooler if flight times stayed the same but the price was a lot cheaper? How cool would it be if you could do cross country for $50, $100 round trip. Want to fly down from NY to New Orleans for the weekend? $20! Now that would be useful. Who cares if a few elite rich people (or business people with big expense accounts) can get across the country in half an hour. I say make the safest form of mass transit (or any transit really) actually available to the masses. Just my $0.02

"Also, the X-15 was dropped from a bomber after being carried to altitude. The SR-71 had its theoretical limits as above. This is a step beyond either--something that would take off on its own and fly faster than the X-15."

Read the article...

"As such, the X-43A will be mounted to an Orbital Science Corp. Pegasus rocket, which boosts the aircraft to the required speed, or about Mach 5 or greater. [...] For the test flight, a modified B-52 bomber with the X-43A attached to the wing will fly to the California coast from Edwards and launch the aircraft along with the booster rocket near San Nicolas Island southwest of Los Angeles. The B-52, built in the 1950s, is one of the oldest around and has been used on some of the most important projects in aerospace history including the air launch of the X-15 and other experimental wingless aircraft."

Also, I don't see where you get that the X-43A doesn't have to carry it's own fuel, either. Even though it gets a rocket powered assist from a rocket that gets a jet-fuel powered assist, it still carries fuel of it's own.

Does this person even know what they are talking about?
First off, the speed of sound is roughly 760 Mi/Hr at sea level, but it depends entirely on the density of the medium the sound is travelling in. At altitude, where aircraft perform best, the speed of sound is roughly 640 mi/hr (again, depending on density).
Production jet powered aircraft have been travelling faster than Mach 2.1 since the 60's. Aircraft, off the top of my head, that travel faster than this are:SR-71, F-14, 15, MiG-23, 25, 29, 31, Su-27, 30, Mirage III, and Panavia Tornado. And that's just the unclassified stuff.

The sonic boom is only produced at the precise moment where the speed of travel for the plane is equal to the speed of sound. At that speed, the sound waves emitted over a period of time "bunch up" and hit together, causing a sonic boom. However, this doesn't apply once the speed gets above the speed of sound - in fact, the faster above the speed of sound that the plane gets, the less of a sonic boom effect it will produce. After Mach 2, the sonic boom effect will be less than if it were standing still.

The shockwave is only a _plane_ when you're at exactly Mach 1. However, you still do indeed get a shockwave at higher speeds. It's a cone instead of a plane, that gets a narrower and narrower aspect ratio as the plane travels faster (the cone expands radially at Mach 1, but the tip [the plane] is moving much faster).

Draw the tip of a stick across still water and watch the ripples to see what I mean. Try this at different speeds (from very slow to very fast).

As it's still a shockwave - an abrupt (discontinuous) change in the velocity and density of the air - it'll still sound like a thundercrack, and will still break windows, because it deposits all of its energy at once (when the shock passes the listener/window).

You'll actually get _more_ damage at higher Mach numbers, because the energy shed into the atmosphere is roughly proportional to the cube of the plane's speed (one of the reasons heating's a problem in hypersonic craft).

It would come after repeated setbacks to design of a hypersonic craft. A $2.5-billion Reagan-era hypersonic program, based in Southern California, was scuttled.

The 80's era project referenced was the X-30 which was also known as the "NASP" or "National Aero-Space Plane". The idea was to have a plane that takes off, boosts to very high speed using SCRAM jets, and finally uses a small rocket boost to reach suborbital velocity. After a cruise above the atmosphere it would reenter to land. The quote that comes to mind is, "New York to Tokyo in two hours."

Unfortunately, like many gov't projects, it ran so far over budget that it was finally canceled. The high speed flight researchers have been trying to recover ever since. The new approach is to use small technology demonstrators to make incremental discoveries rather than putting all the eggs in one basket. Sadly, the gov't didn't learn with the X-33 project which had the same failing.

You are also forgetting that at a ceiling of 100,000 feet the speed of sound is greatly reduced. As well as friction, and other aspects of it.

For example, on the surface of Mars the speed of sound is really slow (180mph, if I recall correctly.. it's been years) and it has the rough equivalency of 180,000 feet (1/3 earth atmospheric density). So for a plane to reach 100,000 feet is quite amazing. Not busting out 5x the speed of sound when the speed of sound is only 900mph.

And, I'm not sure if you realize this but flying a supersonic aircraft requires different aerodynamics than one that flies subsonic. Look at the concord for a good example of this. While flying at supersonic speeds, it is a much more painstaking process to alter your course. Hence, the broad turning radius.

As for the folklore stuff, a lot of that stuff is just rumors and myths. A lot of it is based in fact, but gets the broken telephone effect unfortunately.

And, the reason why 'All this bullshit' is because a plane flying that high is untouchable. Period. Assuming you do pick it up on radar, what are you going to shoot it down with? This plane could be creeping at 200mph at ceiling and it still is relatively safe. It's a surveillance aircraft, they aren't looking to blast over their target so fast they only get a few seconds of images. There was a myth about mounted satellite guns/missiles (heard both) but I have no idea about the validity.

Reinventing the wheel is yet another fine use of our 39% tax bracket that the Clintons invented.

Yeah, after all, it wasn't Ronald Reagan who spent $3.3 billion (just the part not in the "black" budget) on the X-30 National Space Plane scramjet project [fas.org] that never reached a prototype flight. No, it was the Evil Doppelganger Democrat who was really running the White House back then! In fact, while Bill Clinton was Governor of Arkansas, he was secretly controlling President Reagan with his mental emanation telepathy superpowers! Powers Clinton must still be using on Dubya, in an evil plot to make him spend the People's Money (tm), even after January 20, 2001!

The only solution? Aluminum foil wrap around the White House, and tinfoil hats for all Republicans.

By the way, you forgot to include the Clinton Death List (tm). It's not too late to prosecute him for the Lindbergh kidnapping!----lake effect [lakefx.nu] weblog

Logic Bomb seems to be under the impression that The speed of sound is 1000mph. It's more like 730-750mph last time I checked.... Mach 7 is 5000 mph, not Mach 5.

The mph speeds are correct as stated, but all of the mach speeds are off. The SR-71 does go 2100mph, but thats nearly Mach 3, not Mach 2.1. And the new craft in question which will go 5000mph is Mach 7, not 5.

I have no background in aerospace (IANAAE), but I am perfectly willing to believe that a human piloted vehicle moving at mach 5 is too fast to shoot down. Rapid, small changes in velocity (speed & direction) can make its flight path unpredictable; the human pilot can correct for the navigational errors introduced thereby and still get to the target. Since you don't know where it's going to be, you can't shoot it down. And if you shoot at where it is, you'll be shooting at air (unless you're firing a laser).

Ballistic missiles move in a completely predictable path. It's easy (theoretically) to watch them for a second or two, produce a complete model of its ballistic path, and shoot at where it will be.

I see no contradiction. I still don't think anti-projectile defense systems will be effective until energy weapons are used.

Ya what a WASTE of time to fly real fast! Its a shame we throw away money on stuff like that! I mean, who wants to go gallavanting around really fast! And in the AIR too! WHAT MADNESS! If God intended us to fly he'd have given us wings! If God intended us to go faster than 20mph he'd have given us turboprop thighs!

I, for one am OFFENDED that we are wasting money on fruitless projects like flying fast. It would be better spend on expanding the west wing of my 8 bendroom mansion, or paying some immigrant to scrape barnacles off my yacht.

Actually...
though it is true that sound travels faster through dense objects....

The speed of sound through the atmosphere is chiefly regulated by temperature.

The speed of sound at high altitude is quite similar to the speed of sound at sea level, though the amount of drag involved is greatly reduced (this is why the concorde does it's thing at 60,000 feet rather than sea level; too much drag)

Why not just use a rocket the whole way? Assuming the same fuel mass for the scramjet and for the rocket (the efficiencies are way way better for rockets, but we'll give the jet the benefit of the doubt) the oxidizer isn't going to weigh more than the separate engine and fuel system the scramjet's going to require.

Air breathing orbital vehicles are not going to happen anytime soon. The efficiencies just aren't there. Chemical rockets work REALLY well.

1: The P-3 Orion is a plane. Its mission is to spy on people, which is what it was doing at the time of the accident. How is this not a real "spy plane" Its a plane that spys isnt it?

Nope. That's a surveillance aircraft. Spy planes are operated by the CIA and piloted by spies. (most U-2 and some SR-71 missions) By definition, a spy does not wear military uniform, and does not travel in vehicles with military insignia. So, no, the P-3 is NOT a spy plane.

Wouldn't this be useful as the first stage of a two-stage system?

Hellz yeah!

Hellz no. The frontal area of a scramjet is much higher than the frontal area of a comparably powered chemical rocket. Wave drag is a bitch, and it's the factor that will continue to kill air-breathing high speed flight for the forseeable future. The engine is also much heavier than the oxidizer that a regular rocket would use. Remember, you still need a conventional rocket to get this thing up to the point where it can light up...

KISS. Keep it simple, stupid. Scramjets are interesting technology, but they're not going to get me to Mars any faster. Heavy lift orbital insertion is 0wn3rzd by chemical rockets.

Yup. I was very disappointed that NASP and VentureStar were basically boondoggles, although I hope that aerospike engine technology continues to develop. There's a concept that makes a hell of a lot of sense. DC-X did amazing things with vertical landing technology, but I don't buy it as a viable SSTO system. And landing on a rocket in Earth's gravity well Flash Gordon style is totally stupid. The atmosphere is REALLY good at slowing things down...use it!

I make no claims whatsoever about alternative propulsion technologies. I'm not sure I'm ready to believe that giant railguns are going to be a viable launch system, but in conjunction with laser launch systems...mebbe. The Earth's gravity well is a BITCH.

SSTO is not a solution in and of itself. Whatever magic launch system is developed, a staged rocket WILL be more efficient than an SSTO vehicle, in terms of the ratio of fuel weight to payload weight. See, with SSTO, all the plumbing and tanks and stuff that get thrown away from a staged rocket take up weight that could be used for payload.

So, if you can decrease the weight of your structure by an order of magnitude (possible with smart composites engineering, but OBSCENELY expensive) or make enormous strides in engine efficiency (not easy...rockets are pretty damn efficient) SSTO will be possible. SSTO is supposed to win on the maintenance front...it's supposed to be cheaper to refurbish the spacecraft for its next flight than to build another rocket of equivalent power. This goal is the second key to SSTO, and it is far from being realized.

SSTO is not an end in itself. What we REALLY need is inexpensive access to orbit. Some very forward-thinking individuals argue that SSTO is the way to do this, and in the long run they're probably right. I belive that inexpensive rockets are the better alternative, certainly in the near term.

And I AM a rocket scientist. I've got a bumper sticker to prove it. : )

No, there are two valid schools of thought on the subject. I happen to disagree with the people you've talked to...but that's OK. : ) My primary interest is low cost per thrown mass. That favors large, efficient spacecraft (Energia and the big Ariane boosters). I believe that the same engineering advances that make SSTO possible (and don't get me wrong...it IS possible. It CAN be done. I think it's going to be hella expensive though) will allow us to make cheap, expendable heavy lift boosters, with off-the-shelf technology (like Shuttle main engines, which are about the most efficient rocket ever devised).

If you're interested in this subject, check out Robert Zubrin's "The Case for Mars". He describes a heavy lift booster that can carry 1.5-2x the payload of the Shuttle (which is currently the USA's heaviest lift vehicle) and cost much less per shot. I didn't want to believe he was right, but he defends his case admirably.

Rockets are very unsexy, and not very interesting to me. I think they require a sort of brute-force unsubtle engineering approach that doesn't pique my interest the way SSTO craft like VentureStar and DC-X do. However, the economics and efficiency of large rockets for heavy lift are tough to beat.

I do believe that there's a niche for a small, three to six-person reusable spacecraft for moving crew (and passengers?) to and from LEO. I hope that the X-Prize brings some more designs into that arena.

Airline-like servicability is the Holy Grail of SSTO. I don't know if it's feasible. If it were, I'd like to see those principles applied to Shuttle first as a technology demonstrator. (like replace that goddamn heat resistant tile system...those things SUCK to refurbish!)

One interesting proposal I've read is to use throw-away rockets, but have the engine and avionics sections (the expensive parts) be designed to be recoverable and reusable (IE sorta like the Shuttle's SRBs, only cost effective).

Again, reusability isn't the driving factor. If I design a rocket that costs $1000, and it costs you $2000 to refurbish your SSTO craft for a mission, I win. Does that make sense?

The SR-71 uses triethyl borane (TEB) to start. TEB is very volatile and will burst into flames when exposed to air.

Urban legend in the USAF has it that the SR-71 is Mach 4+

Could be... The officially quoted top speed of the SR-71 is "Mach 3+". It all depends on how big the "+" is.

I tend to think that the USAF flew the SR-71 right up to the edge of what it was capable of doing. It was a special-purpose aircraft with highly trained pilots, flying very precise mission profiles. It was designed to do one thing very well (go fast). If it turned out that the SR-71 could go no faster than Mach 3.5 before something horrible happened, I bet the USAF would fly it right at Mach 3.49.

Way back in 1996 on rec.aviation.military, Mary Shaver from NASA Dryden wrote an interesting description of TEB:

TEB is the "igniter" for JP-7. You can't get JP-7 to burn without it in the SR-71, as the ignition of JP-7 takes a higher temperature than
is conveniently produced otherwise. You drop in a shot of TEB, which bursts into very hot flames the minute it has any oxygen, and this ignites the JP-7. Once ignited, the JP-7 keeps burning. The plane has twelve shots of TEB (either total or per engine, I forget), using one shot for each engine start and one for each burner light.

I watched them TEBbing the plane once, keeping well back and being careful to not stand between the big green firetruck and the crew. They had a very, very tiny leak between the TEB nozzle and the aircraft fitting and were getting a drop of TEB released about every 20 seconds. These drops would be on fire as they fell, but they (sort of like most meteorites) burned completely before they reached the ground. It was really pretty, but I was glad it wasn't me in the
silver fire suit.

Well, yes and no... yes, the X-15 went faster than MACH 3, but it did so at considerable expense. It had to be carried up to altitude by a B-52. It used a _rocket_ engine, not a jet engine. On the flights where it pushed the speed envolope most, it ended up losing most of it's verticle tail due to heat burning it off.

My understanding on the SR-71 is that its speed is not limited by engine thrust, but rather by heat buildup. If it goes to fast for to long, it would, literally, melt it's wings and control surfaces off, or at least several damage them. As it is, the plane has literally hundreds of parts that have to be replaced every flight do to the heat killing them. It was designed that way.

Actually, Mach is only one of three measurement commonly used for speed of aircraft. There's Mach, indicated airspeed and actual airspeed, all different. Mach and indicated airspeed are used because that's what the aircraft actually feels. As an aircraft approaches mach 1 (civil airliners cruise at.7-.73 generally) there's something called drag divergence. That's why the civil jets fly at the speed they do, much above that and drag starts to seriously go up exponentially almost. mach varies depending on temperature, not density, but temperature.

Indicated airspeed varies depending on density. For most small aircraft, homebuilts or general aviation aircraft that you and I could fly, this is the most important number as it determines when the aircraft will stall or when the wings will rip off. Mostly used at low speeds when air can generally be considered incompressible. If you go faster where you have to start taking into accoutn compression, then you start dealing more with Mach generally.

And finally actual airspeed which is actually a fixed number no matter where you are, at any location, any altitude, any temperature. But unfortunately, this really doesn't matter to much to the airframe or wings, that's why it's least used, except in planning the actual flight path of the aircraft.

Every window from New Jersey to Nevada was broken today, which officials are at a loss to explain. It appears to have been a sharp earthquake which rattled houses and businesses across the country. Seismologists have reported that every one of their seismographs recorded a large spike, possibly a new type of fault slippage previously unknown.

So the claims of the space shuttle reaching Mach25 aren't that impressive? Does that mean that while in orbit it is effectively orbiting at Mach infinity (as sound has zero propagation speed in space...)?

For some reason I thought Mach was defined as the speed of sound at such a presure and humidity, analogously to c, which is constant, vs the Speed Of Light, which varies.

Why do we use Mach as a measurement of speed when it varies with altitude? No one would ever use a measurement of length that varied with what country you were in? Hmmm... I'll make a measurement called "Schnach" which is 1 meter in Australia, but is 3 inches in the US. Brilliant idea, eh?

NASA never really does anything unless it is forced to do so in order to avoid embarrassment. In this case, it is most likely the amateur rocketeers at the Australian Space Research Institute Scramjet Project [asri.org.au] that are forcing NASA to actually do something other than put women, minorities and geriatric white guys on an infrequently flying Shuttle.

Cargo carriers, such as Federal Express Corp. and United Parcel Service, two of the world's largest freight companies, are intrigued by the prospect of ferrying packages at such high speeds, according to NASA officials.

Hypersonic air cargo systems are unlikely to beat reuseable suborbital cargo systems such as those that have been proposed by Bob Truax [rctruax.com].

The SR-71 has been clocked at a little over Mach 3. Most folks in the business believe it'll go faster.

Rumor has it that no pilot yet has been brave enough to actually put the pedal all the way to the metal. The airframe itself probably limits it to about Mach 3.5 or 3.6; at that point, the shock cone is swept back to where it hits the wing tips, which is a Very Bad Thing.

If I recall correctly, the F-15C tops out at about Mach 2.8, which is pretty impressive for a conventional turbine engine. The former Soviet Union went to great lengths to beat that, the result of which was the MiG-25, which reached Mach 3, but only by using an enormous afterburner that sucked fuel like crazy, limiting such speeds to short bursts.

However, the speed of sound varies proportionally to the density of the medium, in this case, air. So at higher temperatures, and higher altitudes, the speed of sound increases. At the sort of near-space altitudes at which this thing will probably operate, Mach 5 is close to 5000 MPH.

NASA has made two movies of the X-34A (Hyper-X) - one of the separation from the B-52 carrier ship, and another of the flight itself. (MPEG-2 is available, use xine [sourceforge.net] to view on Linux.)

The sonic boom is only produced at the precise moment where the speed of travel for the plane is equal to the speed of sound. At that speed, the sound waves emitted over a period of time "bunch up" and hit together, causing a sonic boom. However, this doesn't apply once the speed gets above the speed of sound - in fact, the faster above the speed of sound that the plane gets, the less of a sonic boom effect it will produce. After Mach 2, the sonic boom effect will be less than if it were standing still.

So, regardless of how fast the plane travels, there will be exactly two moments when there is a "sonic boom" - When it's accelerating and when it's decelerating.

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<whine>
Great. My karma was 50 when I posted the above comment - without the +1 bonus. I got moderated up twice and then moderated down once as overrated and my karma ends up at 49.
</whine>
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I dont buy for a minute that the SR 71 only goes mach 3. What a bunch of crap:) The X-15 (rocket plane) went Mach 6 back in the 50-60s. The MiG-25 FoxBat (similar to F15) does mach 2.5+ (probably more like mach 3). The F-15 does mach 2+. The 16 does mach 2+ on a single engine.

You're telling me the SR-71 only beats these run of the mill jet aircraft by a few hundred miles per hour ?

Bullshit:)

If you buy the discovery channel folklore about the SR-71 (i do:) then it doesn't add up. Pilots wear _spacesuits_. The thing has an operating altitude of 100,000+ feet. Pilots heat their pre-packaged meals by putting the pouch against the cockpit glass. The thing uses special exotic motors and special exotic fuel. (i think its called JP7. Its not flammable. You can apparently fling lit matches into it and they go out. etc etc)

The plane stretches a significant length during flight from heat expansion. its panels and seams are made to expand so much during flight that it _leaks fuel_ when its cold and on the ground. It takes it _several states_ to make a banked turn when flying over the US.

Using a booster rocket, the prototype will be accelerated to mach 5, at which point the pilot's face will be torn from his skull. Hopefully, the plane will fly at speeds up to almost mach 7 for 10-15 seconds before getting hit by a Chinese hotdog pilot.

Doubtful. Supersonic jets bring loud engines and louder sonic booms. This means that such a jet will only be able
to fly out of a handful of airports, limiting the number of planes that will be sold, which limits the price of seats
to the social elite.

What most people dont realize is that at the speeds were talking about (mach 7-10) you can do a nice suborbital hop. This means you thrust to say mach 8 in the atmosphere on a trajectory that will bring you out of the atmosphere. No air means no mach wave which means no sonic boom (contrary to TV and movies, theres no sound in space) The minimum speed for reaching outer space is a bit more than mach 3. its a simple 1/2v^2=gh calculation. of course, youll come straight back down again if youre going this slow, but you will exit the atmosphere. mach 7-10 allows you to gain altitude and speed along the ground. you wont orbit, but youll go quite a ways. Regardless of this, there is still a market for transatlantic and especially transpacific high speed flights. If, and its a big if, you can keep the costs about the same or a little more than conventional planes. If youve ever had to endure a 10 hour flight across the pacific, im sure youd be willing to pay quite a bit more to do it in 2 hours.

1.) Spy planes. And I mean real spy planes, not the glorified P-3 Orion that the press has been quick to call a "spy
plane" recently.:)
2.) Rapid response time. Sure, it may be an engineering problem of figuring out how to shoot at people or drop
bombs on the, but it might be worth it for the 3-4 hour response time to hit just about anybody in the world.

1: The P-3 Orion is a plane. Its mission is to spy on people, which is what it was doing at the time of the accident. How is this not a real "spy plane" Its a plane that spys isnt it?

2: youre right, allegedly people in area 51 have been working on the "45 minutes to anywhere" bomber, who knows if thats accurate.

By definition, a spy does not wear military uniform, and does not travel in vehicles with
military insignia. So, no, the P-3 is NOT a spy plane.

yet it looks like a duck and quacks like a duck, and has the dna of a duck, but its not a duck, ok.

The frontal area of a scramjet is much higher than the frontal area of a comparably powered chemical
rocket. Wave drag is a bitch, and it's the factor that will continue to kill air-breathing high speed flight for the
forseeable future. The engine is also much heavier than the oxidizer that a regular rocket would use. Remember,
you still need a conventional rocket to get this thing up to the point where it can light up...

What do you mean by "frontal area" are you referring to the leading edge? the leading edge of a scramjet is comparable to that of a rocket. Or do you mean the cross sectional area? if so, then yes, the cross section is higher, but this is needed in order for the engine to work.(it has to take in air) Ultimately the fact that air is flowing thorugh part of the cross section tends to reduce wave drag. Your goal is to get to a point higher in the atmosphere where wave drag isnt as much of a problem. A scramjet engine is essentially a box open at both ends. A very specially shaped box, but a box nonetheless. Oxidizer needs to be held in a tank. a tank is also like a box but closed at both ends. Which is heavier, an empty box open at both ends, or a box full of luquid closed at both ends? If you have a hydrogen powered scramjet, you save 8/9 of the wight simply because in a H-O2 reaction, oxygen wighs 8 times more than the hydrogen. You're right, you do need a conventional rocket to get up to speed, and yes this does cut down on the weight savings, but there is still a significant savings.

Ultimately, the military aspects of this are very compelling if it can be made to work. A mach 7-10 cruise missile or surveilance platform would be be very hard to intercept at a reasonable cost. This is what the D-21 drone developed for the SR-71 attempted to do, but the technology wasn't there at the time.

Now, imagine if you will this capability in the hands of 'bad guys'. It makes 100 billion dollars worth of 'star wars' NMD systems in Alaska look pretty stupid, doesn't it? Launch from wherever, take a scenic mach 10 cruise over the mid pacific or the carribean, and 'bang', over the continental city of choice in the mainland US.

You need technology for deterrence, but the only real protection is non-proliferation. That means being cooperative and engaged, not being belligerant and isolationist.

Don't boxers say the same thing? "I wanna dodge, block, or just plain ignore every punch you throw - and I wanna throw punches you can't dodge, block, or ignore at all, sucka!"

I'm sure what you meant to say was "they want a bomber flying at Mach 5 which will be too fast for anybody else to shoot down" and "they want a missile defense system capable of destroying everybody else's theater and ballistic missiles".

You're forgetting that people say "Military Intelligence is an oxymoron" because it's funny, not because it's true. HTH.

So what you're telling me is that with one of these puppies and a parachute I could commute to a job in Silicon Valley from my home in Pennsylvania faster than most of the people who live there? NASA rules.

Yep, this is what I remember about the Foxbat story from the Discovery Channel;-)

The story also said that the CIA fed intelligence to the Pentagon that said the 25 was being made from some wildly exotic composite technology and they postulated all kinds of capabilities that required some kind of counter, the F-15 program.

When Belenko drove his Foxbat to Japan and they took a good look at it, they realized it was constructed of much more conventional materials and so the capabilities that the F-15 were designed to counter were non-existant.

Although the author seems to be confused about the value of Mach 1, some of the responses aren't much more informed. Mach 1 is the speed of sound, which varies greatly depending on the density of the air. At sea level it is usually around 730 mph or so. So it is difficult to say what Mach number the blackbird achieved when it was flying 2,100 mph. You'd have to know the density altitude for the flight. Also, a scramjet engine is not quite the same as a ramjet. The idea is the same, but since air is highly compressible, it behaves differently at different speeds. There are basically four areas of flow: subsonic, transonic, supersonic, and hypersonic. What holds true for supersonic flow is not necessarily true for hypersonic flow. The divisions between these areas of flow depends on the Mach number of the fluid, which is why speeds are rated in Mach numbers and not mph or km/s. So, a different design is required for hypersonic flow compared to supersonic flow. Hope this clears some things up.

You forget that the men that least want to go to war are those that actually have to fight it. They don't want advanced weapons so that they can kill more people faster. They want advanced weapons so that they can scare the enemy enough such that the said weapons are never used.

At sea level, Mach 1 is 760mph. At 40,000 feet it is 660mph. The SR-71 Blackbird has a maximum top speed of Mach 3.54. Her routine altitude is around 250,000 feet. The spacesuits are necessary for the extreme heat, low oxygen, and high stresses of the environment.
The skin does expand when she's on the tarmac, due to the expansion of the titanium skin. JP7 is used for it's high flammability point because of this.
Considering when the Blackbird was built, I'm amazed they got her to go so far, so high, and so fast.

This link (http://www.abovetopsecret.com/aurora.html) has some good background info for those of you who don't know much about the Aurora. Although I can't find links just now. There are several pictures of the "donuts-on-a-rope" contrail and also I heard on TLC a few years ago a story about evidence for sonic booms over the Pacific for which the Aurora is the only really good explanation. So in short yes I do think the government has things that none of us know about. From the fact that this is public knowledge and NASA is doing it we can assume that Mach 5 is nice and slow at this point.:)

The Mach number is not at all a stupid unit. Furthermore it's not a "unit" itself, it tells you the fraction of the speed of sound.
It is a very important number when dealing with aerodynamics, as it will tell you if you are flying subsonic (slower than sound) or supersonic (faster than sound). The airflow around your plane is very different in subsonic and supersonic flow - when you go supersonic shock waves will spread out in a cone starting at the plane's nose. The way lift is generated by the wings is even different sub- and supersonic.
Current (subsonic) airliners can't go faster because of the speed of sound - I think the Boeing 747 cruises at app. Mach 0,8. If it goes faster (into so-called transsonic speeds near Mach 1), shock waves will appear at the upper surfaces of the wings, resulting in high drag and control problems.
It would actually be more complicated to fly these kinds of planes without knowing the Mach number directly, just because it varies.
Ola

For some reason I thought Mach was defined as the speed of sound at such a presure and humidity, analogously to c, which is constant, vs the Speed Of Light, which varies.

Nope. Mach number is defined [about.com] to be relative to the speed of sound in the medium, since that's what is important to an aircraft designer (in terms of calculating stresses and the like).

As for the change in sound speed with altitude, this NASA page [nasa.gov] discusses the physics involved, and links to a neat simulator [nasa.gov] that lets you see how pressure, temperature, sound speed, and the like vary with altitude.

for the basic information and a cool little demonstrator app. However, even at high altitude, the SOS doesn't change much (-14% is "not much" to me). Now, speed of sound through solid rock, THAT'S fast!

One source of confusion is that SOS is about 1100 feet per sec or about 750 miles per hour. People often get the numbers and units swapped.

- Chris

P.S. Wow, I actually used my Aerospace Engineering degree today!

P.P.S. SR-71 has gone to Mach 3 according to public knowledge, but it's widely expected that it went MUCH faster. Hell, most fighter jets can push Mach 2.0, and the SR-71's design point is Speed At All Costs.

And the speed of sound varies inversely proportionally to the compressability of the medium, which in turn varies inversely proportionally to the density and pressure. So you got that right; the speed of sound is proportional to the density of the medium.

But the last part of your argument is backwards; at higher altitudes, the density of air decreases and so does the speed of sound.

I also remember reading somewhere that the speed of sound at 30,000 feet is close to 630mph.

You know how much a billion is? Well, maybe not. It's 10^12 in the Commonwealth countries and 10^9 in the US. (They call 10^9 a milliard).

Interesting, but please cite your source for this. I live in a Commonwealth country (Canada), and while our gallon is different than a US gallon, a billion is most definitely 10^9 here. I knows that cuz I learnt it in skool.

The SR-71 was designed and built by the Lockheed Skunk Works, now the Lockheed Martin Skunk Works. SR-71s are powered by two Pratt and Whitney J-58 axial-flow turbojets with afterburners, each producing 32,500 pounds of thrust. Studies have shown that less than 20 percent of the total thrust used to fly at Mach 3 is produced by the basic engine itself. The balance of the total thrust is produced by the unique design of the engine inlet and "moveable spike" system at the front of the engine nacelles and by the ejector nozzles at the exhaust which burn air compressed in the engine bypass system.

The moveable spike does add a lot of the thrust. But what's being discussed is a scramjet, and as such, it gets all its air without compression. The ramjet is a compromise between the scramjet and the turbojet, really. Also, the ramjet has realistic speed limits, because there is some compression needed to fly, and the craft can't make it to scramjet operational speeds with air-breathing engines.

I'd rant further, but I sold back my propulsion texts when I realized I was going into the church business. Oh well.

Actually, a [the speed of sound] varies with altitude, as temperature and density have an effect on the speed of sound. You can go supersonic, technically, simply by holding speed but changing altitude.

Yes, the SR-71 got to Mach 3+, but not a whole lot faster--the engines were losing efficiency at that point and couldn't push any harder. Even moving the spike in the aerospike didn't help--you were still using some mechanical compression, and the mechanical compression was what was slowing the flow down. Shutting down the turbine blades wouldn't work, either. The theoretical limit is somewhere in the Mach 3.6+ range. I once saw a better analysis, but that was in a book I sold back. =)

But the "been there, done that..." scenario doesn't hold. The X-15 was a rocket plane, and as such had to carry its own fuel. Also, the X-15 was dropped from a bomber after being carried to altitude. The SR-71 had its theoretical limits as above. This is a step beyond either--something that would take off on its own and fly faster than the X-15. Granted, I don't enjoy aerospace engineering anymore, but even I think this is tres cool.

This is important aerospace research, and if you read the article, it's pretty easy to see why. The ability to fly at such speeds for intercontinental, oceanic flights is of great societal benefit. Speed of transport will make this work commercially.

The military aspects are a bit more challenging, though. If you're going to build a bomber so fast it can't be shot down, fine--but then you have to either slow down the craft so that the munitions can exit the slipstream, or you have to come up with some design that will allow you to drop iron at high speeds--such as the Valkyrie, which dropped munitions out the tail.

Either is a huge design problem. If you slow the craft down, you have to design a craft that performs at all speed ranges with in-theater fidelity. If you kick the munitions out of the back, you have to compensate for the mass changes with aerodynamics, because you change the center of gravity all the way through the release profile, and you better hold the craft steady during release, lest you hit the bomb on the way out. "Somebody set us up the bomb," indeed!

But this won't replace STS. Yes, a scramjet is nice. Yes, this is similar to rocket-based combined cycle. But we could more cheaply build a reliable, two-stage system to get into orbit. Mass fractions are all you have to look at to wonder why Single Stage To Orbit [SSTO] is some perverted NASA priority. As a NASA sub, I know they don't live in reality, but damn...

But this is, for once, a positive example of your tax dollars at work.

the mach number is a constant that compressable flow is dependant upon.

you need to complain to god or something. at speeds close to the speed of sound in that medium, the mach number is a very important number. it can be used to very easily characterize the way that the medium will flow around an object.

in aircraft design, an optimum airfoil and engine geometry is characterized by the mach number.

one other technical thing. the mach number is not a unit. that is like saying the number 1 is a unit. the mach number has no units. that is why it is so convenient for engineering. it doesn't matter whether you use metric or imperial.

i can't decide whether you are trolling or just plain stupid, so i'm posting.